Genes and messenger RNAs coding for histones can be isolated from sea urchins. The histonic genes represent as much as 0.5-1% of the total DNA as there are up to 1000 copies of each histone gene in addition to a considerable but as yet undetermined amount of interspersed spacer DNA. Our objectives are two-fold: 1) To learn more about the organization and fine structure of the histone genes, 2) To investigate the transcription of this DNA both in vivo and in vitro. The analysis of fine structure would include a determination of linkage between the genes coding for the various histones, measurement of spacer size and position, and determination of extent of sequence conservation among the repeating units. We will employ the techniques of restriction enzyme mapping, denaturation mapping, heteroduplex studies and prehybridization, linkage analysis for these experiments. Transcriptional studies would include a determination of extent of regulation of RNA synthesis in vivo, a search for possible nuclear precursors to histone mRNAs, and studies with chromatin to see if the in vivo controls of RNA synthesis can be maintained in vitro. These experiments are now possible since the isolated histone DNA can be used as a hybridization probe for newly synthesized histone mRNA sequences.